The invention relates to a cylinder head gasket installed between two engine members such as a cylinder head and a cylinder block of an internal combustion engine to seal therebetween.
When joint surfaces between the cylinder head and the cylinder block (a cylinder body) of the engine in an automobile are sealed, a cylinder head gasket is installed therebetween to seal combustion gas, cooling water and the like.
Due to demands for lighter weight and lower cost of the automobile engines, a structure of the cylinder head gasket has been shifted to a simple type formed of a single metal base plate from a laminated type having a number of metal plates. As the simple type structure is made of a single plate, only limited types of materials can be used.
In the laminated type metal plate gasket, a sealing member such as a bead, grommet and shim can be combined as necessity and provided in double for effective sealing. However, in the single plate gasket, a kind and a number of sealing members are limited, so that a simplified sealing device has to be used. Moreover, an area available for the sealing device is limited due to reduction in an engine size.
As shown in FIG. 1, the cylinder head gasket is formed for fitting to a shape of an engine member such as a cylinder block. The cylinder head gasket includes holes 2 for cylinder bores; fluid holes 3 for circulating cooling water and engine oil; bolt holes 4 for tightening bolts; and a gear box hole 5 and the like. Also, sealing devices, such as beads 12, 13, are provided with respect to the respective holes to be sealed.
Although one single gasket is used to seal between the engine components, different sealing properties are required to seal the different holes. For sealing the cylinder bores 2, it is required to seal the combustion gas with a high temperature and a high pressure, while a fluid with a relatively low temperature and a low pressure needs to be sealed at the fluid holes 3.
An arc shape bead 12 with a narrow width, which is formed of an elastic material for fitting to an irregular surface, is provided around the cylinder bore 2. Also, the cylinder bore 2 is surrounded by the bolt holes 5. Bolts are inserted into the bolt holes 5 to tighten the cylinder head and the cylinder block by applying a large pressure.
A bead 13 is provided around the fluid hole 3 to seal the same. Depending on a structure of the engine, there is a case that the fluid hole 3 is formed outside an area surrounded by the bolt holes 5. In this case, the pressures of the tightening bolts are applied on only one side of the fluid hole 3, thereby reducing the tightening force. To solve the problem, a higher bead, a narrower bead, or a pointed bead has been used.
Further, to seal a small uneven surface like a tool mark or the like formed on a sealing surface of the engine member, such as the cylinder head and the cylinder block, micro sealing coatings made of rubber, such as NBR rubber and fluoro rubber, are applied to entire surfaces on both sides of the gasket.
Since the micro sealing coating generally has a pencil hardness of 2H-4B and a thickness of 10 xcexcm-30 xcexcm, the micro sealing coating has a sufficient sealing effect with respect to a small uneven surface in an order of 5 xcexcm-15 xcexcm, such as a tool mark left on the sealing surface of the engine member. However, the micro sealing coating can not effectively seal a slightly larger uneven surface like a V-notch and a step with a 20 xcexcm-50 xcexcm depth.
Especially, in a case that a relatively large scratch formed on the surface of the engine member crosses a sealing line formed of the bead or the like, a part of the scratch is not sufficiently sealed. Thus, the combustion gas, cooling water or oil may leak.
The leaking problem by the scratch such as a V-notch on the sealing surface of the engine member has been a serious problem. This is because a relatively soft and fragile metal such as an aluminum alloy has been used for an engine member to reduce a weight of the engine. Also, even slight leak of the combustion gas, cooling water or oil needs to be prevented.
In view of the above problems, the present invention has been made. An object of the invention is to provide a cylinder head gasket formed of a single metal base plate or multiple plates, wherein the cylinder head gasket has a plurality of sealing lines having proper hardness, thereby being able to seal a relatively large scratch formed on the surface of the engine member. Further, a plurality of the sealing lines provides the metal gasket with a resistance against flow and torque down, thereby obtaining a good sealing ability and durability.
Further objects and advantages of the invention will be apparent from the following description of the invention.
In order to attain the above objects, a cylinder head gasket of the present invention is structured as follows. The cylinder head gasket is formed of a single metal base plate for sealing between two components, wherein both sides of the metal plate are coated with micro seal coatings. At least a pair of sealing lines is formed of seal coatings with a thickness larger than the micro seal coating on flat portions of both sides of the metal plate. A position where one of the sealing lines is formed on one side of the metal plate is shifted relative to a position where the other of the sealing lines is formed on the other side of the metal plate.
Here, the flat portions are areas where no uneven surface associated with a full bead or no step/slant surface associated with a half bead is formed. Also, at least the pair of the sealing lines is formed on both sides of the metal plate, wherein at least one sealing line is formed on one side of the metal plate and at least one sealing line is formed the other side of the metal plate. That is, the sealing lines are paired with respect to both sides of the metal plate. Accordingly, there may be a case where odd number of the sealing line(s) is/are formed on one side and even number of the sealing lines is formed on the other side.
The cylinder head gasket may be formed of laminated multiple metal base plates for sealing two components, wherein both outer sides of the metal plates are coated with the micro sealing coatings. At least a pair of sealing lines is formed of sealing coatings with a thickness larger than the micro sealing coatings on the flat portions on both sides of the metal plates. A position where one of the sealing lines is formed on one side of the metal plate is shifted relative to a position where the other of the sealing lines is formed on the other side of the metal plate.
In the above-mentioned metal gasket, the sealing coating is a foamed coating formed of silicone, and the micro sealing coating is a rubber coating made of fluoro rubber or NBR rubber.
That is, the foamed seal coating is made of a foamed synthetic resin like a silicone resin containing micro capsules, and is coated by a screen printing to form the sealing line having a thickness of 40 xcexcm-150 xcexcm, a width of 0.5 mm-5 mm and a hardness more than 2B in pencil hardness. The micro seal coating is made of fluoro rubber or NBR rubber, and is coated on both entire surfaces of the gasket by a screen printing to form a thin coating having a thickness of 10 xcexcm-30 xcexcm and a hardness H to 2B in pencil hardness.
According to the structure described above, since the seal coatings are provided on the surfaces of the gasket where an engine component contacts, a sufficient sealing effect is achieved with respect to a scratch, such as a V-notch, larger than a tool mark formed on the sealing surface where the gasket contacts.
Further, the positions where the sealing lines of the sealing coatings are provided are shifted between a front side and a backside. Thus, the number of the sealing lines is increased, thereby improving the sealing effect.
Further, the micro seal coatings are provided on the surfaces where the seal coatings are applied, and both sides of the seal coatings are sandwiched and fixed. Thus, the seal coatings are prevented from flowing.
Also, the seal coating is provided on an area where there is no uneven surface of the bead, thereby causing no negative effect on a function of the bead. Further, the sealing line is provided separate from a sealing line provided by the bead, thereby improving the sealing effect.